Proportional scale



A. M. CLARK 1,8l0;392

PROPORTIONAL SCALE Filed June 6. 1929 June 16, 1931.

ATTORNEY.

Patented June 16, 1931 PATENT OFFICE ARTHUR CLARK, 0F SEATTLE, WASHINGTON PROPORTIONAL SCALE Application filed June 6, 1929.

This invention relates to drafting instruments and has special reference to a copying instrument for enlarging and reducing maps, charts and all types of drawings.

One important object of the invention is to provide an improved instrument of novelconstruction and affording a rapid and con venient means to aid in the reproduction of drawings and prints to enlarged or reduced scale. I

A second important object of the invention is the provision of a novel drafting scale for this purpose.

A third important object of the invention is to provide a novel arrangement of straight edge to which selected scales may be applied to permit enlarging and reducing of drawings in any desired ratio.

lVith the above and other objects in view as will be hereinafter apparent, the invention consists in general of certain novel details of construction and combinations of parts hereinafter fully (:lescribed illustrated in the accompanying drawings and specifically claimed.

In the accompanying drawings like characters of reference indicate like parts in the several views, and:

Figure 1 is a plan view of the complete apparatus showing the method of using the same. i

Figure 2 is an enlarged plan view of a portion of the pivot end of the straight-edge.

Figure 3 is a section on the line 33 of Figure 2.

In the construction of the invention as shown herein there is provided an ordinary drafting-board or table 10 which may be of any preferred size or construction and may also be either portable or stationary. This board or table will be hereinafter referred to as a board but it is to be understood that by this term is meant any of the usual constructions having a surface to which paper or the like for drafting is adapted to be secured.

To this board is pivotally attached the straight-edge which forms the principal part of the invention and this straight-edge consists of a strip 11 of suitable material such as wood, metal composition or the likeand Serial No. 368,823.

this strip is provided with at least one straight drawing edge 12, and so constructed that scales 14 may be retained by any suitable means.

At what may be termed the zero end of this straight-edge there is provided a lateral lug 16 so that an opening 17 may be formed therein on the line of the straight-edge 12 prolonged. In this opening is seated suitable means, such as the pin 18 for securing the straight-edge pivotally on the board 10. Now, it will be noted that the pivot center of the straight-edge or blade is the zero point of all the scales to be used with the instrument. Consequently the graduations on these scales do not begin with a zero mark but, as shown in Figure 2, with a numbered mark. In any event two sets of graduations are used and these may either be shown on the same scale strip or the upper strip may be transparent and carry one set of graduations while the lower strip carries a second set. The two sets of graduations used have their unit distances in the ratio desired for enlarging or reducing and in the present showing these ratios are 2/3 and 3/2 according as to whether the operation is to be a reduction or enlargement. Obviously other scales may be used giving other ratios so that reduction or enlargement on any desired ratio may be obtained.

In Figure 1 is shown the method of using the invention. In this view a map to be enlarged and a sheet on which to draw the enlargement is indicated at B. Suppose a line my to exist on the small map. The map and blank sheet are fixed on the board in oriented relation and the straight-edge is swung until its edge 12 is coincident with one end of the line my and the indication. of the smaller scale noted. As here shown such indication will be 16.3. Then at the point 16.3 of the larger scale, this being on the blank sheet, a dot is placed as at X. Similarly, the point 3 is noted on the smaller scale and laid off at 05 Y on the larger scale. Then a line drawn from X to Y will represent the line my enlarged. Obviously, any number of points on one drawing may thus be located on the other. Furthermore, reversal of the read- 10 inns will eflect a reproduction in reduction.

It to be noted that the principle here used is that of similar geometric figures having equal angl es and adjacent sides proportional.

There has thus been provided a simple and eliicient device of the kind described and for the purpose specified.

It is obvious that minor changes may be made in the form and constr ction of the invention Without departing from the material spirit thereof. It is not, therefore, desired to confine the inventimi to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

Having tints described the invention, what is claimed. as new, is:

1. An enlarging and reducing instrument including a straie'ht-ede e having an edge provided with a piurali' oil" interchangeable scales having their zero points in common, said scales extending in the same direction from the zero point and having their scale divisions all extending to the same edge of the straight-edge.

.2. An enlarging and reducing instrument including a straight edge having an edge provided with a pair of scales having their Zero points in common and having graduations of different unit lengths, one of the scales being of trans ian'ent material and overlying the other.

in te;.

llilOllj f whereof I aiiix my signature.

Ali-T'l-lUl-l M. CLARK. 

